Focus on text field on load (iPhone)

Hello! Can anybody help me with such a problem? I want to set focus on text field while level is loading and display iPhone keyboard. I thought that this approach will work, but it's not or I did something wrong:

private Rect userNameTextRect;
private string userName = "";

...

void OnGUI()
{
    GUI.SetNextControlName ("UserName");
    userName = GUI.TextField(userNameTextRect, userName, 10); 
    GUI.FocusControl("UserName");
}

This code works only on desktop for me, but on iPhone TextField is not focused. Can anyone give me some suggestion how may I solve this problem?

Found some approach (not the best, but appropriate in my situation):

private iPhoneKeyboard keyboard;
private string userName = "";

void  Start ()
{
    keyboard = iPhoneKeyboard.Open(userName);
}

void  OnGUI ()
{
    userName = keyboard.text;
    GUI.Label(userNameTextRect, userName);
}